327 Small Block Chevy Engine Build - The 500HP Question

For This 327, The Answer Is Yes-And Then Some

Often the hunt for horsepower starts with a question. You know the type: "Hey, I made 480 hp-how much more would I have to do to make 500?" That's exactly the query posed by Jeff Latimer of Valencia, California's JGM Performance Engineering, who had a good combo in hand: a small-block throwing down 420 lb-ft of torque to go with all those ponies. What makes the question compelling, though, is that those numbers came from a "mere" 327. So when we learned that JGM had teamed up with its neighbors at Air Flow Research to deliver an impressive reply to the 500hp question, we didn't have to be asked twice to check out the results.

Latimer is a staunch 327 fan. "It's part of my memory from the good ol' days of Pro Stock," he told us. "Everybody was running them." So later on down the road, he built one: a 10:1, hydraulic flat tappet motor with duration at 0.050 in the 240s, and wearing AFR 180 Eliminator heads. No question, he was impressed with the result. They're great numbers for a 327-but you know where this is heading.

The foundation was another 327 block. When outfitted with ARP studs, the factory two-bolt mains were more than sufficient for the planned power level. The mains were also precisely line-honed and the bearing clearances set with the factory steel crank being utilized. The holes were bored 0.040 over; with the standard 3.250-inch stroke in place, displacement came out at 333 ci. The reciprocating assembly was fairly pedestrian: Eagle 6-inch I-beam rods topped with KB hypereutectic slugs. "They're enough for 500 hp," Latimer explained. The short-block is more than adequate, but nothing exotic, as our builder puts it.

The wealth of experience at JGM, along with some computer modeling based on cylinder head flow data and estimated cranking compression, led to more particulars. The chosen cam was an aggressive Comp solid-roller, boosted with Comp 1.6:1 Hi-Tech stainless steel rocker arms. Also of note is the piston deck height-the +0.005 figure, when combined with the cylinder heads' 60cc chamber volume, creates a fairly tight quench figure of 0.035 inch, which promotes efficient combustion.

Latimer was impressed by the performance of the 180 Eliminator heads on his first 327, and he naturally turned to Tony Mamo and the AFR crew for help in answering the 500hp question. The heads of choice were a set of the company's 195 Competition Ported Eliminators. Mamo put it in a nutshell: "Jeff and I felt these heads were ideally suited to this project, 'cause we intended to turn it pretty hard."

"Ideally suited," indeed: The horsepower goal was blown away by a good 10 percent, as in 50-plus more horsepower than the goal. Peak power came at a not totally astronomical 7,100 rpm. And as impressive as 553 hp is from a 327, check out the torque numbers. Right off the bat, 433 lb-ft at 5,600 isn't a bad peak. But this thing's at 380 lb-ft by 3,900 rpm, and stays over 400 from 4,600 all the way to 7,200 rpm. It's a screamer-but one with an impressive and flat, useable torque band. "That's why we used the 195 Comp ported heads," reiterated Mamo. "Since this engine will spend more time on the street than at the track, we were concerned about the bottom end and throttle response as well as the top end power."

Latimer is thrilled with the results, especially, we suspect, with that flat torque curve, since this mill could find a home in the '63 Chevy II he's been working on. On the other hand, more questions have already arisen, and Latimer admits that he might have used some different components if he'd known he was going to exceed the 500hp goal by so much. He's already working on it, and of course the question has already been posed: "I wonder how much more it'll make next time?"

Quick NotesWhat We DidFollowed along on a mission to obtain 500 hp from a 327 small-block

MORE PHOTOS

Ignition duties were handled by a standard GM HEI distributor, suitably enhanced with an MSD Digital HEI Module and Coil. The setup handled 7,500-plus rpm without any issues.

Three subtly different intake manifolds were tried during dyno testing. One was an out-of-the-box Super Victor, while the others were fully ported Super Victors from different sources. The mysterious black lung on the right was part of the high-horsepower combo.

Although headers with larger-diameter tubes were tried, best results were achieved with Hooker 1 3/4-inch Super Comp long-tubes, fitted with 18-inch extensions.

A peek down the valley during an intake change revealed the Comp solid-roller lifters, as well as the Manley 5/16-inch pushrods. These pieces have a 0.080-inch-thick wall for improved valvetrain stability. And while many 195cc runner heads match up to a Fel-Pro 1205 intake gasket, AFR's Mamo pointed out that the Comp ported head is closer to the larger 1206 gasket.

We already mentioned that best power numbers were obtained with the black ported intake-fitted with a stack of phenolic spacers. The four-hole spacer was added first to add to the plenum volume; the potent 327 picked up about 6 hp.

A tapered combo spacer was then added to this intake sandwich. This type of spacer helps get the mixture flow out of the carb, filling in dead air spots and eliminating backswirl, according to Mamo. This one picked up another 2 hp. Latimer's Chevy II has a cowl hood on it, so he can actually fit these spacers underneath if he chooses to.

Two carbs were used on this 327, and the highest horsepower number was obtained with this AED Performance 950 HO carb. AED buys unmachined castings from Holley, then does all its machining in-house, does precise parts matching, and installs its own fuel curve and calibration, among other features. The 950 HO actually uses a 750-cfm HP body combined with an 850-cfm baseplate. Real-world flow, according to AED, is 825 cfm. The larger baseplate allows airflow for power up top, while the smaller body enhances responsiveness since the venturi controls the signal to the boosters.

The AED mixer came out of the box with 78 primary jets and 86 secondaries-this 327 liked things on the lean side for its most powerful dyno pulls, so the front side was pulled back four sizes to 74, while the secondary side was cut back two sizes to 84.

To obtain a compression ratio in the 11.5:1 range, the heads were milled down 0.030 inch, reducing the chamber size from 65 cc to an even 60 cc. About the chamber: Mamo called it an "efficient heart-shaped design that helps low and midlift flow." Below about 0.400-inch lift, the chamber is more important than the port in promoting flow, since the mixture must get past the valve. After that, the valve is farther away, and the chamber is less critical.

According to AFR, its Comp ported heads feature a finer level of CNC work, allowing for entirely accurate reproduction of the original port design. This is evident in the intake ports, which also feature a ramp or air dam of sorts in the intake bowls, which Mamo said "does some very beneficial things for the airflow curve in general." Never one to mince words, he added, "It's the most efficient port design out there in a medium-sized 23-degree cylinder head."

The exhaust ports also receive the same precise CNC treatment as the rest of the head, but lack the wings found on the intake side. They do, however, have a generous short term to allow the burnt junk an unhindered exit path.